The thing I like the most is the animated trainer and pokemon sprites. I always can't wait to fight the next gym leader or see a new pokemon, because I love the way they move.
And I like the battle frontier and the move tutors. I hate getting shards just to learn moves, because I'm lazy. I will eventually find a way around that through hacking shards, or if not, I'll take my butt underground.
I have fought some of the battle frontier in Emerald and hated most of it, and in Pearl, beated Palmer 4 times, so I can't wait for this, because I have matured since Emerald came out, and think it would be useful.